It is known that hydrogen is the gas used for supplying the fuel cells that make up high-yield electricity generators. The generalization of the use of fuel cells should contribute to reducing the greenhouse effect.
The generation of hydrogen that is needed for fuel cells or for other industrial applications can be obtained by reacting a hydrocarbon and water. The hydrocarbon that is most often used for producing hydrogen is natural gas (mainly consisting of methane, but also ethane or propane), in a catalytic vapor reforming reactor. However, hydrogen may be produced from other hydrocarbons as well, and in particular such petroleum cuts as diesel fuel, naphtha, kerosene, gasoline, liquefied petroleum gas (propane, butane), and such biofuels as the biogases, vegetable oils and their esters, ethanol or methanol, adapting the temperature conditions and the catalysts to the hydrocarbon and to the process, which can be a vapor reforming, a partial oxidation or even an autothermal vapor reforming.
Hydrogen is generally produced in two steps.
During a first step called “reforming,” the carbon of the hydrocarbon is combined with the oxygen of water to provide mainly carbon monoxide CO and to release hydrogen. Then, during a second step, the carbon monoxide CO is again combined with water to provide carbon dioxide CO2 and hydrogen H2.
The reforming operation that produces CO+H2 is an endothermic reaction, i.e., a reaction, to which heat must be provided. To this end, an exothermic reaction is used, which consists of the combustion of a fraction of the hydrocarbon flow with a flow of oxygen. Thus, a fraction of the hydrocarbon constitutes a fuel for providing heat and the complementary hydrocarbon fraction constitutes the main reagent which will provide the hydrogen. Therefore, it is understood that the burned hydrocarbon fraction must be minimized to maximize the reformed hydrocarbon fraction.
The reforming gases are produced at high temperature and the heat that they contain can be recovered for preheating the fluids entering the reaction chamber, or reagents, i.e., the water, the hydrocarbon and the flow of oxygen (which may be the oxygen of the air or pure oxygen, or even a mixture). Thus, the reforming reaction is carried out with hot reagents, which makes it possible to reduce the burned hydrocarbon fraction.